The above patents disclose a composition horseshoe or horseboot having a sole and a somewhat flexible envelope for surrounding the horse's hoof below the coronary band. The envelope has a pair of re-entrant folds one on each side wall of the envelope on an upper portion of the side wall. Tensioning means engaged either external brackets having a plurality of outwardly directed projections for adjustability or internal grooved means such as a cable slip or pulley. The boots are snugged to the horse's hoof using a center toggle buckle to tighten the cable and compress the envelope about the hoof. In the later version, a strap around the rear of the hoof is provided, and downwardly slanting projecting barbs protrude from the internal brackets on either side to provide non-slipping engagement with the side walls of the horse's hoof when the shoe is snugged on the horse's hoof.
This arrangement is satisfactory, but has some disadvantages that are addressed by the improvements of the present invention. In the configuration shown in U.S. Pat. No. 4,174,754, the side plates and rear serrated strap are rigidly fixed to the side walls of the boot. This has the effect of limiting the size of hoof that the boot will fit, since the distance from the back of the serrated strap to the front or "toe" of the boot is fixed. In practice, this limitation has made it necessary to stock several sizes of boot to ensure appropriate fit.